Adjustable potentiometer termination



2 Sheets-Sheet 1 A TTORNEK Sept. 22, 1953 H. L. COYNE ETAL ADJUSTABLE POTENTIOMETEIR TERMINATION Filed Dec. 15, 1950 H. L. cor/v5 8y 0. s. ,4. MESCH S M w w w FIG 2 Sept. 22, .1953 H. L. COYNE ETAL 2,653,207

ADJUSTABLE POTENTIOMETER TERMINATION Filed Dec. 15, 1950 2 Sheets-Sheet 2 FIG. 4

/-/.L. cor/v5 WVENTORS 0. S.A.ME$CH ATTOPNEV Patented Sept. 22, 1953 ADJUSTABLE POTENTIOMETER TERMINATION Howard L. Coyne, Rockville Centre, N. Y., and Orwar S. A. Mesch, Morristown, N. J assignors to Bell Telephone Laboratories, Incorporated, New York, N. Y., a corporation of New York Application December 15, 1950, Serial No. 201,044

Claims. 1

This invention relates to electrical measuring or controlling devices of the potentiometer type and, more particularly, to such devices which utilize a slide-wire unit comprising a length of resistance Wire and a contact-making member or arm adapted for sliding engagement therewith.

The ideal resistance unit for a potentiometer of the self-balancing type should consist of a bare wire of resistance material so disposed that the sliding contact or arm may engage any point along its length and that the length thereof would be precise and of an exact value. However, du to the physical difiiculties of obtaining suitable resistance values within the available dimension-a1 limits, it is seldom that this ideal can be obtained without resorting to complicated mechanisms which, in themselves, tend to introduce errors that oifset the precision attendant 0n the use of the continuous bare wires.

In potentiometers of the self-balancing type, it is usual, therefore, for the slide wire or resistance unit to be in the form of a continuous Winding on a card or mandrel, with the turns of wire along one edge thereof exposed for contact with a sliding arm or contact member at successive turns. By the use of a very fine wire and a great many turns, the potential drop between successive convolutions may be made so small that a single step, that is, from one turn to the other, or a momentary short-circuit between turns is not preceptible in its effect on the apparatus in the circuit of which the potentiometer forms a part.

In resistance devices in which a resistance wire is wound in a plurality of turns on a support, it is sometimes found necessary in order to obtain predetermined precise resistance values to tap the resistance wire at precise points instead of simply connecting ends of the resistance wire to terminals and using the whole length of resistance wire as a resistance element. The point of tapping may have to be so precise that a particular turn of the resistance wire must be tapped.

It will be appreciated, therefore, in constructing potentiometers of the self-balancing type that it is highly desirable to construct the resistance unit in such a manner that a precise over-all resistance value is assured and that some means should be provided for adjusting the value or efiective length of the resistance unit after it has been assembled between terminations thereon. I

.It is an object of the present invention to provide a potentiometer of the circular slide-wire type in which the terminals thereon may be adjusted after the potentiometer is assembled to obtain a precise value between the terminations.

In accordance with one preferred embodiment of my invention, I provide a circular potentiometer with variable terminations which comprises a casing, an arcuate slotted member positween the contact member on the frame and.

the potentiometer wires on the card is assured by suitable spring members on the frame which bear on the slotted member and force the frame member upward so that the contact member thereon firmly engages the wires on the resistance member. Apertures are provided in the wall of the potentiometer casing, whereby a suitable tool may be inserted to engage the inner edge of the bottom portion of the frame so that either a clockwise or counter-clockwise rotation imparted to the tool will cause the frame to slide in its arcuate slot and either increase or decrease the resistance by altering the position of the termination.

In another form of the adjustable termination dveice of this invention, a circular member is provided on the interior of the potentiometer casing beneath the card and is provided with a plurality of continuous arcuate-shaped slots on its upper surface so that a plurality of contact carrying frames may be positioned therein for obtaining varying terminations on the potentiometer card at different points along its length. Suitable apertures are provided around the periphery of the potentiometer casing for the insertion of a tool therein to adjust the contact frame.

The invention will be more clearly understood from the following detailed description when,

read in conjunction with the accompanying drawings, of which:

Fig. 1 is a perspective view of a potentiometer illustrative of this invention, with parts broken away to expose the resistance winding and the adjustable termination in contact therewith;

Fig. 2 is a sectional View taken on line 2-2 of Fig. 1;

Fig. 3 is a top plan view, partly in section, taken on line 3-3 of Fig. 2;

Fig. 4 is an'elevational View, with parts broken 3 away, of another embodiment of the invention in which a plurality of adjustable terminations may be positioned to make contact with the winding of the resistance wire along its length;

Fig. 5 is across-sectional View taken on line Fig. 6 is. a perspective view, partly in section, of the guide member for the adjustable terminations;

Fig. 7 is an enlarged perspective;yiew'icti the;

adjustable termination contact frame;

Fig. 8 depicts a simple circuit.employing the. potentiometer as shown in, Fi'g. Land utilizing? one adjustable termination. at, g. the; end oi; the resistor unit;

Fig. 9 shows a circuit employing the potentiometer shown in Fig. 4 and utilizes 'an adjustable deredverticaily extending central bore l5 which i'spin register withan aperture 16 in the bottom ofthe casing I.

: As shown in Fig. 2, thesleeve 14 extends upw'ardly some distanceabovefthe edge of casing l0 and has secured thereto, on its periphery, a slidewire resistance unit, I l, which comprises a spirally wound card or mandrel Ifljhayingwoundthereon in anunbrokenlengthgand in'a djacent convolutions'a resistant wire 19.. .The t'u'rns ofthe card [8." are separatedfro-m. each other by the spiral partition. or separator '20 which. is continuous in length and which as shown,.extends some distance. above andbclow the cardli8 and is con! struoted of suitable insulating material. The 'resistance unitll,jwhich comprises the "spirally woundcard [8 with the resistance wire ,I9wound thereon. and the insulated separator or partition ZO'is clamped togetherto form; a unitary structure by the band or clamp 2|, as shown.

Botatably mounted in the central bore Ijof the sleeve I A: andextending throughthe aperture l6 jin the casing iii and. beyond. the upperend of the sleeve M is the operating shaft 22. As shown in detail in, Fig. 2, the shaft .22 ispjrovided at its lowerend withsuitable means ilillior rotating the shaft, and a suitable cover plate. 24 isalso secured thereto. There is also provided suitable stop nieans which'comprises. the worm 25, the. travelling washer it; the fixed washers 2T,and.28;,and theirassociated. stop pins 29,30,

and 31. These pins cooperate to limit the revcilutions of the shaft as it is operated in either a clockwise or counterclockwise direction.

Fixedly secured to the shoulderedportion. on the upper end of the shaft 22, betweenthe washers 32 and 33, by means of the nut 34.15 a radially extending, contact carrying arm. 35. This. arm is constructed of insulatingmaterial. and has mounted on its. free ends. pair ofcontact brushes 36 and 31. Brush 3% is adapted v to engage the upper. surfaceoffthe resistance wire I9"on the card It and guided thereon by means of thepartition 20,.and the. brush 3'] frictionally engages the collector ring 38". which. infturn is connected to a. lead-in wire (not-shown). 'connected to the bindin post terminal 39 located on the exterior of the casing H], as shown. This structure provides a variable electrical connection to the resistance unit ll anywhere along the length oi the. card. One, end .oi the. vresistance wire l9=onthe card lmwhich makes'u the resistance unit i1, is connected to the binding post .,terminal 40 by a suitable lead-in wire (not shown), and the other end of the resistance unit isz-leitunconnected "In5order to provide an accurate and precise termination for the unconnected end of the ref. srsnancejumm I, avaliable or adjustable termina- I, tionisprovidedwhich permits the effective length oLthe'resistanoe-wire [9 to be accurately adjusted within very close limits.

H I As shown in Figs. 1 a um; there is provided on the bottom I I of the casing lfl an arcuate shaped member 4| which is constructed of suitable insulating material and is provided with anarcuate slot 42. The, slot..." isof.substantial"depthgand isadaptedto s rceivethe arcuate shaped frame memh (shown in Fig. 7), jwhichcarries a contact pin d 'don its upper edge. Theframe R3113 ail to ireely slidein slot 42' and. is. forced upward to; cause the contact i'n 44' to frictionally. engage the. resist'ance wirei l9 by meansoi. the spring members 45 and 46' which bearagaihstf the top surface of the arcuate member. and cause the contact: pm 4 4 "on the' frame 43 be forced' upwardly into contact with the resistance in 9 as shown. A suitable lead-in fwir 14] is attached to. the frame..,43 'and'in' turn is cohnectedfto. the

. bindingpost 148. on the exterior di the casing shown. in Fig. 1.

In order. to adjust thejvariable.termination of this invention, a suitable tool" is iiisertedjlin. the aperture 49' adjacent the framelli; andsince' theend of the tooljis taperedi itjwiltrlde'f ie-r the inner bottomedgeofthe' rr meand c au the contact pin, 44 to be movedidownward'ou of engagementj with the resistance wire l9. The tool.

thenmay beflrotated either. clQGKWiSeor counterclockwise, and due to the frictional engagement of theitoolwith the lower inner edge,..o-f the' frame, itwill' cause the'frarn'eflt andthe contact All associated therewith to be;rnoy'edln the grooveeither in a clockwise orIcounten-blbckwise direction. dependingupon thejrotation of thetool;

Q It .will jbe obsery'ed that the end termination or the resistance wire may be precisely adjusted to providethe desired. resistance value. After the adjustment is mad'e ,.the apertureQthrough' which meteor has been inserted, may be closed by Iain suitable means, for, example, a. screw. Asshown in Figs. land 2;,a suitableycoverinl i'spro-Vided to protect theijinstrument.

In, fanothe r' embodiment, of the. invention, ,as shown in. Figs. '4, 5', and theregi's'providedia housing or casing ,5l havinga plurality ofjspaced.

apartv aperturesfll on its periphery which. extend. through the wall. thereof and communicate with the interior ofthe casing 51 (as,shofwn..mo-re in detail in Fig.5).

Likethe structure illustrated Figs. 1,2. and3. and described hereinabove, v there is provided insulating sleevemember 53 which is, secured to the'bottorn of. the casing. 52,. and. extends. above. the edge thereof. It has 'mountedthereona resistance' unit 54 which comprises as'tructure substantially, the same as that shown. in and, described in detail with respect toEigs. 1, 2., and 3. and j 'is, provided with an electrical connection. t orn thelrotating arm, the contacts of which. are

5. in sliding engagement with resistance wire 55 on the resistance unit 54, to the binding post terminal '56 located on the exterior of the casing The embodiment of this invention, as shown in Figs. 4, 5, and 6, differs from the structure heretofore described with respect to Figs. 1, 2, and 3 in that neither end of the resistance wire 55, which makes up the resistance unit 54, is permanently connected to a binding post terminal. The unit is provided with adjustable terminations both at its ends and mid-way between its ends to provide precise and accurate values of resistance, as will hereinafter be described in detail. 5

As shown in Figs. 4, 5, and 6 and particularly in detail in Fig. 6, there is provided on the bottom of the casing 5|, surrounding the sleeve member 53 and spaced away from the resistance unit 54, a ring member 5'? of insulating material. The ring member 51 is provided with coaxial grooves or slots 58, 59, and 60. As shown, each slot is of substantial depth and may have slidably positioned therein a frame member 61 having an upstanding contact 62 projecting upwardly therefrom and in frictional engagement with the bottom surface of the resistance wire 55 of the resistance unit 54.

Each of the frame members 6| has a lead-in wire 63 connected thereto, which in turn is connected to a respective one of the binding post terminals 64, 65, and 66 on the outside of the casing 5|.

As heretofore described with respect to Figs. 1 and 7, the frame members 6| are provided with suitable spring members 61 and 68 which bear against the upper surface of the member 51 and force the contact pin 62 into intimate frictional engagement with the bottom of the resistance wire 55.

The frame 6| may be positioned at any point within the confines of its respective slot or groove and may be moved clockwise or counter-clockwise by inserting a tool, as heretofore described with respect to the structure shown in Fig. 1, through any one of the apertures 52 which is in register with the respective frame, thereby providing not only a variable termination at each end of the resistance unit 54 but a variable midtap connection independent of the adjustable contact arm. The latter is adjustably rotated by means of the shaft connected thereto as heretofore described. Suitable closures, for example, the screws 69, are provided for the apertures 52 when the adjustment has been completed.

As shown, a suitable casing is provided to protect the interior of the device from dust and dirt.

Fig. 8 shows one application of the potentiometer shown in Figs. 1, 2, and 3 which utilizes a single variable termination and its application to a simple circuit.

Fig. 9 shows a simple circuit in which the structure shown in Figs. 4, 5, and 6 is used and in which a variable termination at one end of the resistance unit and a variable connection mid-way between the ends of the resistance unit i provided.

Fig. 10 shows a simple circuit which utilizes the structure of Figs. 4, 5, and 6 to obtain variable terminations at each end of the resistance unit and at a point mid-way between the ends thereof.

While we have shown and described preferred embodiments of the invention, it is to be understood that various changes and modifications may be made therein without departing from the spirit of the invention.

What is claimed is:

1. In an electrical resistance device comprising a card of insulating material and a resistance wire wound in a plurality of convolutions on said card, an adjustable brush in engagement with said resistance wire, a casing, means in said casing for supporting said card, a supporting member positioned in said casing in juxtaposition with respect to said card and having guide means thereon, a contact member comprising a frame and a contact, means biasing said contact against an edge of said card, for making contact with the resistance wire on said card, said frame being slidably positioned on said supporting mem-j ber and confined in the plane of said card by said guide means, a lead-in wire for establishing an electrical connection, secured to said contact member, said contact member adapted to be moved along said resistance wire, to vary the termination thereof.

2. In an electrical resistance device comprising a card of insulating material and a resistance wire wound in a plurality of convolutions on said card, an adjustable brush in engagement with said resistance wire, an apertured casing, means in said casing for supporting said card, a supporting member positioned in said casing and having an aperture therein in alignment with an aperture in said casing, in juxtaposition with re spect to said card and having guide means thereon, a contact member slidably positioned on said supporting member and confined by said guide means, for making contact with the resistance wire on said card, a lead-in wire for establishing an electrical connection, secured to said contact member, said contact member adapted to be moved along said resistance wire, to vary the effective length thereof.

3. In an electrical resistance device comprising a card of insulating material and a resistance wire wound in a plurality of convolutions on said card, an adjustable brush in engagement with said resistance wire, an apertured casing, means in said casing for supporting said card, a supporting member positioned in said casing below said card and having an aperture therein in alignment with an aperture in said casing, and having guide means thereon, a contact member slidably positioned on said supporting member and confined by said guide means, for making contact with the resistance wire on said card, a lead-in wire for establishing an electrical connection, secured to said contact member, said contact member adapted to be moved along said resistance wire, to vary the effective length thereof.

4. In an electrical resistance device comprising a card of insulating material and a resistance wire wound in a plurality of convolutions on said card, an adjustable brush in engagement with said resistance wire, an apertured casing, means in said casing for supporting said card, a supporting member positioned in said casing and having an aperture therein in alignment with an aperture in said casing, in juxtaposition with respect to said card and having guide means thereon, a contact member comprising a frame and a contact, means biasing said contact against an edge of said card, said contact having a knife edge adapted to forcibly engage said resistance wire, said frame being slidably positioned on said supporting member and confined in the planelofa saidcardibyg,said guide. means, a lead in: Wire, for. establishing; an electrical connection, secured to said contact member said; contact member adapted to be moved along said;resist ance wire to vary thetermination thereof.

. v5:; In an electrical resistance device comprising: a=card of insulating material and a resistance wire wound in a plurality, of convolutions onlsaid" card, an adjustable brush inv engagement. with said resistance wire, an apertured casing; means in; saidz casin'g for supporting said card; a. supporting member positioned in said casing and having an aperture thereinin? alignmentrwithl an aperture in said casing; in juxtaposition with respect to said cardand having guidemmeansthereon, a contact member comprising a frame and a contact, means biasing said 'contact against an-edge of saidfcard lsaid contacthaving a knife edge adapted to forcibly engage said-l resistance wire Said frame; being, slidably; positioned! on said sugporting-v member and-confined im the plane; of 1 said card by; saidguide means and having a follower surface in alignment with. saidapertures adapted to be, en-

gaged by means, inserted. in said apertures for moving said contact member; along said resist-l ance wire, and v a, leaq in wire for establishing an electricall coxmection secured to said con-tact:

Number Date Name Klosner J an 13; 1925- 

